Gasoline pump multiplexer system for remote indicators for self-service gasoline pumps

ABSTRACT

A multiplexer system employing a form of pulse width modulation and detection. The system is particularly adapted to use in a telemetering system for remote indicators. The system operates in connection with a self-service gasoline pump and transmits via a 60 Hz. powerline gallons and dollars information. A modified form of the system transmits only dollars or only gallons information for a plurality of pumps. The system can be further adapted for inventory control purposes. Variants include signal forcing and totalizing circuits for a plurality of independent information sources providing absolute accuracy.

MiG-870,15 5?? m2 sisal S36 United Stal Prosprich 2, Feb. 8, 1972 [54]GASOLINE PUMP MULTIPLEXER 3,376,744 4/1968 Kister et a1 ..235/92 FLSYSTEM FOR REMOTE INDICATORS 3,510,630 5/1970 Ryan et a]... ..222/76 FORSELILSERVICE GASOLINE PUMPS 3,243,800 3/1966 Probert.... ...340/203 [72]Inventor: hank B. Prosprlch, West Hartford, Conn.

[73] Assignee: Veeder Industries Inc., Hartford, Conn.

[22] Filed: Apr. 14, 1970 [21] Appl. No.: 28,379

[52] US. Cl. ..340/203, 340/206, 340/184, 340/310, 235/92 FL, 222/23[51] Int. G08c 19/16 [58] field oISearch ..340/203, 206, 310, 182, 184;222/26, 23, 76; 235/92 FL, 92 AC, 151.34; 73/194 [56] References CitedUNITED STATES PATENTS 3,229,300 1/1966 Thompson et a1. ..340/310 PrimaryExaminer-John W. Caldwell Assistant Examiner-Robert J. MooneyAnomey-Prutnnan, Hayes, Kalb & Chilton ABSTRACT A multiplexer systememploying a form of pulse width modulation and detection. The system ispartiailarly'adapted to use in a tleinetering system for remoteindicators. The system operates in connection with a self-servicegasoline pump and transmits via a 60 Hz. powerline gallons and dollarsinformation. A modified form of the system transmits only dollars oronly gallons information for a plurality of pumps. The system can befurther adapted for inventory control purposes. Variants include signalforcing and totalizing circuits for a plurality of independentinformation sources providing absolute accuracy.

15 Claims, 10 Drawing Figures mentions 8 912 3.641.536

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GASOLINE PUMP MULTIPLEXER SYSTEM FOR REMOTE INDICATORS FOR SELF-SERVICEGASOLINE PUMPS SUMMARY OF THE INVENTION The invention generally relatesto multiplexer and telemetering systems, and is of special significanceto a remote control system for one or more gasoline pumps at a fillingstation in which signals reflecting the operation of each pump areconducted on the 60 Hz. powerline to a control point inside the station.

Most multiplexer systems in common use generally employ frequency oramplitude modulation techniques or a combination of both. Where theintelligence to be transmitted in the several channels is fairly complexor broadband, these systems are highly suitable. However, in thoseapplications involving the most simple form of information, i.e., on oroff, frequency and amplitude modulation techniques as applied tomultiplexing become too complicated when compared to the data to betransmitted. Furthermore, in the transmission of elementary on-off data,reliability is of utmost importance. Noise, therefore, becomes anincreasingly important factor inasmuch as noise-induced frequency andamplitude variations on transmissions can cause serious error in anaccumulated total at the receiver. Pulse modulation techniques areuniquely suited to the transmission of this type of information.Multiplexing of simultaneously occurring pulse data usually requiressome form of elaborate bufier memory system in order to avoid losingbits of data. As a result, this type of system becomes prohibitivelyexpensive for many applications.

A simple pulse multiplex data transmission system is particularly usefulin a self-service gasoline station wherein data pertaining to each pump,such as dollar amount of sale and total gallons, is supplied to acentral pay booth which would require only one attendant. In addition,such a system may provide a means of automatic inventory control.

It is therefore an object of the present invention to provide a simplepulse data multiplexer system.

It is another object of this invention to provide a multiplexer andtelemetering system for a dispensing system.

It is a further object of the instant invention to provide a gasolinepump multiplexer system with remote indicators for a self-servicegasoline station.

It is yet another object of the invention to provide a multiplexersystem for a dispensing system which incorporates an inventory control.

Other objects will be in part obvious and in part pointed out more indetail hereinafter.

A better understanding of the invention will be obtained from thefollowing detailed description and accompanying drawings which set forthcertain illustrative embodiments and are indicative of the various waysin which the principles of the invention are employed.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a pictorial illustration showing gasoline pumps in a remotecontrol service station;

FIG. 2 is a block and schematic diagram of a sender unit in themultiplexing system according to the invention;

FIG. 3 is a block and schematic diagram of a receiver unit for themultiplexing system according to the invention;

FIG. 4 is a timing diagram useful in understanding the operation of thecircuits shown in FIGS. 3 and 4;

FIGS. 5A and 5B are simplified schematic diagrams which illustrate ascheme for obtaining a stable signal at the receiver over a powerlineregardless of load variations and noise on the powerline;

FIGS. 6A and 6B are block diagrams illustrating modifications of thesystem according to the invention which are useful in transmitting priceonly information or in inventory control;

FIG. 7 is a logic diagram illustrating the circuitry of the parallel toserial converter and one-bit memories in FIGS. 6A

and 6B; and

FIG. 8 is a timing diagram useful in understanding the operation of thelogic shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS .Briefly stated, the presentinvention provides a simple pulse multiplexing system which generatestwo difi'erent pulses which represent, for example, gallons and dollars.Pulsers representing fractions of a dollar and fractions of a gallon ofgasoline provide inputs to a modulator which includes oneshotmultivibrators that act to switch difi'erent timing resistors into themodulator. Each one-shot switches a switch to gate a burst of carrierfrequency of a fixed duration such as 20 ms. The dollar pulser providesa pulse for each cent and operates through the modulator to cause theswitch to produce a burst of spaced pulses which are ON 1.9 ms.throughout the 20 ms. burst. The gallons pulser operates on the OFFcycle to provide a burst of spaced OFF pulses of 1.9 ms. for the 20 ms.interval. The pulses can overlap partially or entirely. This results ina system which is neither frequency nor amplitude sensitive but ratheris sensiti cjo thgpulsewidth o f the ON or OFF pulses. In afiif irfirversion, the invention is useful in a system which operates to telemeterprice or gallons information only. A modification of this systemcontemplates the telemetering of gallons information from a plurality ofpumps to a central station where the information is totalized forpurposes of inventory control. Incorporated into this system is aparallel to serial converter having simple one-bit memories to bufi'erthe input data from the several pumps.

Referring now to the drawings, wherein like reference numerals refer toidentical or similar structures throughout the several views, FIG. Igenerally illustrates a self-service gasoline station which employs thegasoline pump multiplexer system according to the invention. Such astation typically comprises a plurality of gasoline pumps 10 on each ofthe several service islands 11. Typically, a customer 13, upon alightingfrom his vehicle 12, removes the nozzle 15 from its support, turns thehandle 14 to reset the computer and proceeds to dispense gasoline intothe tank of his vehicle 12.

Data, such as gallons dispensed and price of sale, are transmitted to aremote station 16, which may be conveniently located at the exit ramp ofthe service station, and after filling the tank of his vehicle 12, thecustomer replaces the nozzle 15 of pump 10 on its support and proceedsto the station 16 where the attendant on duty then looks at a displaypanel, collects the indicated amount in his remote control panelcorresponding with the pump used by the customer.

For purposes of illustration only, the electronics of the multiplexersystem is shown as housed in a box 18 supported above the service island11 by a pole 19. The pole 19 serves as a conduit for wires that connectthe multiplexer system to the mechanism of pump 10. Box 18 is shown asconnected to the service station 16 by the normal 60 Hz. powerlines 20which supply power to the pump motors of the pumps 10 and signalsbetween the box 18 and the service station 16 may be by way of carriermodulation superimposed on the 60 Hz. powerline frequency although otherforms of transmission may be employed.

The basic multiplexer system of the invention employs a form of pulsewidth modulation and detection in which the canier is switched on andoff, effectively producing a resultant wave form analogous to percentsquare wave modulation. At a given carrier frequency, by varying both ONand OFF times and employing 0N time and OFF time recognition circuitryat the receiving end, it is possible to transmit two distinctive signalssimultaneously. FIG. 2 of the drawings illuscent. These pulse inputstrigger respective one-shots 21 and 22 which produce output pulseshaving a fixed duration of, for example, ms. The output of one-shot 21is connected to one input of AND-gate 23 which in combination with NPN24 forms an electronic switch. The output of one-shot 21 is alsoconnected to one input of AND-gate 25. In like manner, the output ofone-shot 22 is connected to one input of AND-gate 26 which incombination with NPN-transistor 27 forms another electronic switch. Theoutput of one-shot 22 is also connected to the second input of AND-gate25. The output of AND-gate is connected to the second input of AND-gates23, 26 and to the base of NPN-transistor 29 to provide a thirdelectronic switch.

Each of the three electronic switches just described are used to controlthe period of a square wave generator 30 which is preferably an astablemultivibrator. Generator 30 comprises two programmable unijunctiontransistors (PUTs) having their cathodes connected in common to groundand their anodes connected by a timing capacitor 33. The gate electrodeof PUT 31 is connected to a voltage divider comprising resistor 34 andresistor 35 connected in series across a source of positive voltage andground. Similarly, the gate electrode of PUT 32 is connected to avoltage divider comprising resistor 36 and resistors 37 and 38 connectedin series across the source of positive voltage and ground. A timingresistor 39 is connected between the anode of PUT 32 and the source ofpositive voltage. A switchable timing resistance 40 is also connected tothe anode of PUT 32. Three switchable timing resistances 41, 42 and 43are connected to the anode of PUT 31. Timing resistor 41 is connected tothe emitter of transistor 24, timing resistor 42 is connected to theemitter of transistor 29, and timing resistors 40 and 43 are connectedin common to the emitter of transistor 37.

A pulse at the gallons input triggers one-shot 21. As shown at the topof FIG. 4 of the drawings, this pulse enables AND- gate 23 which causestransistor 24 to conduct. Transistor 24 is biased into saturationeffectively connecting timing resistor 41 to the source of positivevoltage. Under these conditions, the astable multivibrator 30 begins tooscillate, producing a series of pulses at the gate electrode of PUT 32as represented by the modulation envelope shown in FIG. 4. The value oftiming resistor 41 is selected such that the duration of the outputpulses is relatively short, say 0.7 ms., compared with the intervalbetween pulses which might be 1.9 ms. If, on the other hand, a pulse atthe dollars input triggers one-shot 22, AND-gate 26 and transistor 27will conduct with the result that tinting resistors 40 and 43 areeffectively connected to the source of positive voltage. The values oftiming resistors 40 and 43 are chosen such'that the pulse pattern outputat the gate of PUT 32 is just the opposite of that produced by a pulseat the gallons input, that is the pulse would be 0N for 1.9 ms. and OFFfor 0.7 ms. This is shown at the right-hand part of the modulationenvelope illustrated in FIG 4. It is possible for the pulses produced byone-shot 21 and one-shot 22 to overlap. When this happens, the output ofAND-gate 25 causes transistor 29 to conduct and inhibits AND-gates 23and 26. This in turn causes timing resistor 42 to be effectivelyconnected to the source of positive voltage. The value of timingresistor 42 is chosen such that a symmetrical pulse pattern output isproduced at the gate electrode of PUT 32. In other words, the output ofastable multivibrator 30 during this overlap period will be a series ofpulses 1.9 ms. in duration separated by intervals of L9 ms.

A Colpittis oscillator 44 with good temperature stability is used togenerate the carrier. The output of oscillator 44 is connected to thebase of PNP-transistor 45 which is connected as an emitter follower. Theoutput of emitter follower transistor 45 is connected to the base oftransistor 46 which acts as a gated buffer amplifier.

Resistors 37 and 38 form a voltage divider which is connected to thebase of NPN-transistor 47 which in combination with PNP-transistor 48comprises an electronic switch. The collector of transistor 48 isconnected to the base of transistor 46, and when transistor 48 conducts,transistor 46 is biased to nonconduction. When transistor 48 is off,transistor 46 passes the output of oscillator 44 to the input of poweramplifier 49.

The power amplifier 49 provides sufficient line drive to overcome theeffects of powerline loading at the carrier frequency, deliveringapproximately milliwatts to the line through a line coupling network 50.The coupling network 50 comprises a coupling transformer 51 havingprimary and secondary windings. A capacitor 52 is connected across theprimary of coupling transfonner 51 to form therewith a tank circuitresonant at the carrier frequency. Relatively broad tuning is employedin the primary circuit, and care is taken to ensure a clean undistortedcarrier signal on the line to avoid harmonic sideband problems. Smallcoupling capacitors 53 and 54 presenting a high impedance at thepowerline frequency are employed for isolation in series with thesecondary of the output transformer 51. Interposed between thesecoupling capacitors and the secondary winding of transistor 51 is aresistance network comprising a shunt resistance 55 and two seriesresistances S6 and 57. A neon indicator lamp 58 may be connected acrossthe output to the powerline.

The series resistances 56 and 57 may be described as current or signalforcing resistances and have as their objective to ensure a stablesignal at the receiver over the powerline regardless of load variationsand noise on the powerline. FIG. 5A shows in simplified schematic formthe relationship of the current forcing resistance 56 to the circuitryof the system. The sender which is shown in FIG. 2 may be consideredanalogous to a current generator 59. Resistance 56 is placed in serieswith the current generator 59, and a receiver 60 is connected to acurrent transformer 61 placed across the powerlines in series withcapacitor 62. Resistance 56 has a value chosen sufficiently high so thatcapacitor 62, which serves as a high frequency short across thepowerlines, produces a substantially constant current output for aninformation signal delivered to the receiver 60 regardless of-variationsin the line loading and noise. Also shown in FIG. 5A is a filtercomprising a choke coil 63 connected in series with the powerline and acapacitor 64 connected in shunt with the powerline. The filter isolatesthe signal from the remainder of the powerline so that the informationis not conducted to the right of the filter. Not only will this preventpossible information from being available to a competitor who might beconnected to the same powerline, but it also makes it possible to usethe same powerline for carrying other signals at the same carrierfrequency from a difi'erent sender when another gasoline pump isconnected to the powerline. The filter could be eliminated in thesituation where a different canier frequency is used for each gasolinepump and where the power transformer for the station is relied upon toblock the pickup of information by a competitor from the powerline.

A variation of the current forcing technique shown in FIG. 5A isillustrated in FIG. 5B. In this case, three senders represented bycurrent generators 59a, 59b and 59c are each connected in series withcurrent forcing resistances 56a, 56b and 560, respectively. Each ofthese current generators and their series connected resistances areconnected in shunt with the powerline. The receivers 60a, 60b and 60cfor each of the different signal generators are powered by the samepowerline. The current transformers 61a, 61b and 61c which pick up theinput signal for each of the respective receivers are placed on the samepowerline shunt.

It should be noted at this point that while the invention has so farbeen described as senders located at gasoline pumps and receiverslocated at a central station, it is also possible to provide a signalgenerator at the central station and a receiver at the pump islands forresetting the computer and turning the power on and ofi at each pumpfrom the station. The same powerlines could be used for a plurality ofpumps, and the same carrier frequency could be used for controlling eachpump as is used for transmitting information such as dollars and centsfrom the pump to the station.

Referring now to FIG. 3 of the drawings, the receiver is connected tothe powerline by a coupling network 65 similar to that used at theoutput of the sender. Coupling network 65 comprises a couplingtransformer 66 having primary and secondary windings. Connected inseries with the primary winding are a pair of coupling capacitances 67and 68 each of which is connected in series with a resistance 69 and 70,respectively. A neon indicator lamp 71 may be connected in shunt withthe powerline. Connected in parallel with the secondary winding ofcoupling transformer 66 is a capacitance 72 which together with thesecondary winding of the transformer forms a parallel resonant tankcircuit. The tank circuit is resonant to the carrier frequency.

When more than one pump is connected in the system, it is desirable tohave a high Q tank circuit for selectivity between pumps, i.e., betweenoscillator frequencies. However, a high Q results in the slow buildupsof the signal and ringing or slow decay. This, of course, seriouslydistorts the pulse envelope. In order to limit the effects of ringing ofthe tuned coupling circuit and provide good selectivity, the tankcircuit is connected to the input of a logarithmic preamplifier 73. Asis known in the art, the property of such an amplifier is to amplifysmall amplitude signals greater than large amplitude signals. This hasthe effect 0 squaring up" the input pulse burst. The output of thelogarithmic preamp 73 is connected to a tuned amplifier 74 whichprovides additional gain and selectivity. This output is connected to athreshold detector 75 which detects the pulse modulation envelope. Thepulse output of detector 75 causes a switch comprising NPN-transistor 76and PNP- transistor 77 to be turned on and ofi synchronously with thepulse modulation envelope.

The output of the switch is connected to a first pulse withdiscriminator 78. This discriminator comprises at its input a pair ofNPN-transistor 79 and 80 which are connected in cascade. Transistor 79is turned on by an ON pulse from transistor 77. This in turn causestransistor 80 to be turned off. Connected in series across a source ofpositive voltage and ground are a timing resistance 81 and a chargingcapacitance 82. The junction of resistor 81 and capacitor 82 isconnected to the collector of transistor 80, and when transistor 80 isbiased to nonconduction, capacitor 82 is charged through resistor 811.If the pulse output from detector 75 is of sufiicient duration,approximately 1.9 ms., capacitor 82 will charge sufficiently to tire afour layer threshold device 83 connected thereacross.

A load resistor 84 is connected in series with four layer thresholddevice 83 and the voltage produced across this load resistor is appliedto the base of NPN-transistor 85. Transistor 85 in combination withPNP-transistor 86 forms an electronic switch which controls anothertiming circuit comprising timing resistance 87 and charging capacitance88 connected in series with the collector of transistor 86 and ground.If the pulse appearing at the base of transistor 85 is too long,capacitor 88 will charge sufficiently to fire four layer thresholddevice 89 connected thereacross. Otherwise, capacitor 88 is dischargedthrough resistor 87 and resistor 90.

The four layer threshold device 89 is connected in series with a loadresistance 91, and the voltage developed thereacross is applied to thebase of an NPN-transistor 92. The emitter of transistor 92 is connecteddirectly to ground and the collector is connected to a source ofpositive voltage by a resistor 93 and a firing capacitor 94 connected inseries. The junction of resistor 93 and capacitor 94 is connected by wayof an isolating diode 95 to the collector of transistor 85. Whentransistor 85 conducts, capacitor 94 is discharged through transistor 85and resistor 94a. If the pulse at the base of transistor 85 is not toolong, transistor 85 will turn off allowing capacitor 94 to be chargedthrough resistor 93. The charge accumulated on firing capacitor 94triggers a retriggerable or integrating one-shot 96. If, on the otherhand, the pulse at the base of transistor 85 is too long, then fourlayer threshold device 89 discharges capacitor 88 providing a pulse atthe base of transistor 92 which conducts and prevents capacitor 94 fromtriggering one-shot 96. So long as the pulses applied to the input ofthe integrating one-shot 96 are of sufficient duration, the output ofthe one-shot will remain on. Thus, the one-shot 96 provides an outputhaving a duration of 20 ms. as shown at the bottom of FIG. 4. Thisoutput is used to drive the counter driver and counter 97 which in thespecific example is the dollars counter.

The gallons information is detected in a similar manner with anidentical pulse width discriminator 98 and integrating oneshot 99.However, since the gallons information is represented by OFF pulsesrather than ON pulses, an inverting transistor 100 is connected betweenthe switch comprising transistor 76 and 77 and the pulse widthdiscriminator 98. The output of integrating one-shot 99 is applied to acounter driver and counter 101 which is the gallons counter.

It may be appreciated from the foregoing discussion that the pulse widthdiscriminators 78 and 98 operate to reject both short duration pulses,such as characteristic of transient noise, and long duration pulses,which might be generated during equipment turn off and turn on, and toidentify only the desired pulse. A signal sensing circuit 102 may alsobe provided. This circuit would be connected to the output of detector75 or the switch comprising transistors 76 and 77 and would serve toenable the counters 97 and 101 only when a carrier is present. Thesignal sensing circuit then provides protection against false countingsince a discriminator output alone cannot initiate the counter driveunless the sensing circuit 102 is on.

In the embodiment described it is assumed that both gallons and dollarinformation are to be transmitted. There are many applications whereonly dollar information or only gallon information are needed to betransmitted. These possibilities are shown in FIGS. 6A and 6B of thedrawings which illustrate a four channel system transmitting onlydollars information or only gallons information. In this situation adifferent carrier frequency for each pump is selected. Since only oneitem of information is to be transmitted, only one one-shot 21, forexample, is required. The output of one-shot 21 gates a switch 103 whichsupplies power to a square wave generator 30. The output of square wavegenerator 30 gates the output of oscillator 44 through switch 46 topower amplifier 49. The output of power amplifier 49 is connected to thepowerlines 104 through a coupling network 50. The powcrlines 104comprise a three conductor 230 volt line having the center conductorgrounded. One hundred and fifteen volt service is thus available acrosseither of the two outside lines and the grounded centerline. If desired,a filter comprising series connected choke 63 and shunt connectedcapacitance 64 may be interposed between the powerline and the couplingnetwork 50.

At the receiver end, a coupling network 65 couples the signal on thepowerline to a log preamp 73 and tuned amplifier 74. Threshold detector75 receives the output from tuned amplifier 74 and provides a detectedpulse output to pulse width discriminator 78. Since only one item ofinformation is being transmitted by a particular pump, only one pulsewidth discrirninator is required. The output of discriminator 76 isapplied to integrating one-shot 96 which provides a counting pulse tocounter 97. A separate counter 97 is provided for each pump at thecentral station when only dollar information is to be transmitted.

In applications where the information desired is the total number ofgallons sold from a plurality of pumps, the outputs of each of theintegrating one-shots 96, representing quantity delivered by each of thepumps, are applied to a parallel to serial converter and one-bitmemories 105 which provides an output to a totalizing counter 106.

A schematic representation of a logic circuit suitable for providing theparallel to serial converter and one-bit memories 105 is shown in moredetail in FIG. 7 of the drawings. Each of the one-shots 96 from the fourchannels is applied to respective flip-flop memory 107. The output ofone-shot 96 is also applied to one input of a three input AND-gate 109.The output offlip-flop 107 is applied to another input of AND-gate 109.The AND-gates 109 are each strobed by a clock 110 applied to their thirdinput.

Clock 110 comprises a clock oscillator 111 which produces a symmetricalsquare wave output as illustrated at the top of FIG. 8. This square waveoutput is applied to inverter 112 in order to shift the phase of theoutput 180 The phase shifted clock oscillator output is then applied toa counter 113 which in its simplest form may be a four stage ringcounter. Counter 113 produces a four phase clock or strobe which appliesa pulse to one-shots 108 to produce a pulse of short duration (ascompared to the duration of the strobe pulse) which is applied to theAND-gates 109 at uniform intervals as illustrated in FIG. 8 to ensurethat pulses are evenly spaced at input of OR- gate 115. The frequency ofclock oscillator 11 l is sufi'lcient to strobe each AND-gate 109 twicefor each input pulse from its one-shot 96.

In operation, if a pulse is generated by one-shot 96 at a time whenthere is no strobe input to AND-gate 109 from counter 113, flip-flopmemory 107 will be set. The output of flip-flop 107 enables AND-gate 109until it is reset. When a strobe pulse later appears from counter 113 itis passed by AND-gate 109 to trigger one-shot 114. The output ofone-shot 114 resets flip-flop 1M and is also connected to OR-gate 115.OR-gate 115 is a four input OR gate, receiving one input for eachchannel in the system. The output of ORgate 115 sets a flip-flop 116.Flip-flop 116 is reset by the output of clock oscillator 111. Thus,flip-flop 116 is caused to toggle back and forth with a frequency thatdepends upon the rate at which gallons information is applied to all ofthe several channels of the system. The outputs of flip-flop 116 areeach connected to respective driver circuits 117 and 118. These drivercircuits each are operative to energize a respective winding 119 or 120of a stepper motor 121. The stepping motor 121 has a mechanical outputdrive which drives the totalizer counter 106.

Where a pulse is generated by one-shot 96 at the same time as there is astrobe input to an AND-gate 109 from counter 113, AND-gate 109 will notpass a signal to trigger one-shot 114 and the pulse is not then passedto OR-gate 115. Neither is flip-flop 107 reset. However, since thefrequency of clock oscillator 111 is sufficient to strobe AND-gate 109twice for each input pulse from one-shot 96 at the maximum pulserepetition rate of the pulsers in the pumps, counter 113 will cycletwice between the receipt of two consecutive bits of information fromthe same source. As a result, on the next cycle there will be no outputpulse from one-shot 96 and the strobe pulse from counter 113 will bepassed to trigger one-shot 114 and reset flip-flop 107. Thus, onlyone-bit memories are required to prevent the loss of any bit ofinformation thereby ensuring that the total count at counter 106 isaccurate.

In its most comprehensive form, the invention would comprise thetransmission of both dollars and gallons information as particularlydescribed with respect to FIGS. 2 and 3. In addition the system wouldalso include a totalin'ng output for either dollars or gallons or both.For example, it is possible to provide the attendant on duty in thestation with price information from each pump andat the same timeprovide total gallons information for purposes of inventory control.

As stated previously, it is also possible to provide a sender at thestation and a receiver at each pump. This is illustrated in FIGS. 6A and613 by the blocks 122 and 123 labeled reset." Block 122 in this casewould be a sender and block 123 would be a receiver similar to thosedescribed in detail with respect to FIGS. 2 and 3. The purpose of such aprovision would be to allow the attendant to have complete control ofthe pumps from the station. Specifically, the attendant could use theresets to make power available at the individual pumps only when hewishes to authorize a customer to use the pump.

As will be apparent to persons skilled in the art, variousmodifications, adaptations and variations of the foregoing specificdisclosure can be made without departing from the teachings of thepresent invention.

1 claim:

1. In a dispensing system having at least one dispensing apparatus whichis capable of generating separate triggering pulses corresponding tofractional parts of at least two different units of measurement relatedto the dispensed product, a multiplexer system comprising:

a pulse width modulator responsive to one of said triggering pulses forgenerating a series of pulses having a first duration separated byintervals having a second duration, said pulse width modulator alsobeing responsive to another of said triggering pulses for generating aseries of pulses having said second duration separated by intervalshaving said first duration, and said pulse width modulator further beingresponsive to the simultaneous occurrence of the two triggering pulsesfor generating a series of pulses having said first duration separatedby intervals having said first duration,

a gated carrier frequency oscillator connected to said pulse widthmodulator and providing a pulse modulated output,

transmission means receiving said pulse modulated output from said gatedcarrier frequency oscillator for transmitting the modulated signal to acentral point,

receiver means at said central point for receiving the transmittedsignal and providing a detected output,

pulse sorter means connected to receive the detected output from saidreceiver for providing a first output in response to a series of pulseshaving said first duration and a second output in response to a seriesof pulses separated by intervals having said first duration, and

indicator means connected to each of said first and second outputs ofsaid pulse sorter means for providing an indication at the central pointwhenever either of said triggering pulses occur.

2. A multiplexer system as recited in claim 1 wherein said pulse widthmodulator comprises:

an astable multivibrator, and

switching means responsive to said triggering pulses for selectivelychanging the time constants of said astable multivibrator.

3. A multiplexer system as recited in claim 2 wherein said astablemultivibrator includes a plurality of timing resistors and saidswitching means further comprises:

a first one-shot triggered by one of said triggering pulses forproducing a pulse output having a fixed duration substantially longerthan both said first and second durations,

a second oneshot triggered by another of said triggering pulses forproducing an output pulse having a duration equal to that of the outputof said first one-shot,

a first electronic switch connected to the output of said first one-shotand operable to connect a first combination of said timing resistancesto said astable multivibrator,

a second electronic switch connected to said second oneshot and operableto connect a second combination of timing resistances to said astablemultivibrator,

an AND gate receiving as its inputs the outputs of both said first andsaid second one-shots and providing an output only when the outputs fromsaid first and second oneshots are coincident, and

a third electronic switch connected to said AND gate and operable toconnect a third combination of timing resistances to said astablemultivibrator.

4. A multiplexer system as recited in claim 1 wherein said pulse sortermeans comprises:

first and second pulse width discriminators each operable to detect apulse having said first duration, one of said pulse width discriminatorsreceiving the detected output from said receiver means and the other ofsaid pulse width discriminators receiving the inversion of the detectedoutput from said receiver means, and

first and second integrating one-shots connected to the output of saidfirst and second pulse width discriminators, respectively.

5. A multiplexer system as recited in claim 1 wherein said dispensingapparatus is a gasoline pump and said units of measurement are dollarsand gallons, respectively, and said indicator means provides numericalreadouts of the number of gallons dispensed and the dollar valuethereof.

6. A multiplexer system comprising a pulse width modulator responsive toa first-data pulse for generating a series of pulses having a firstduration separated by intervals having a second duration, said pulsewidth modulator also being responsive to a second data pulse forgenerating a series of pulses having said second duration separated byintervals having said first duration, and said pulse width modulatorfurther being responsive to the simultaneous occurrence of said firstand second data pulses for generating a series of pulses having saidfirst duration separated by intervals having said first duration,

a gated carrier frequency oscillator connected to said pulse widthmodulator and providing a pulse modulated output,

transmission means receiving said pulse modulated output fortransmitting the modulated signal to a remote point,

receiver means at said remote point for receiving the transmitted signaland providing a detected output,

pulse sorter means connected to receive the detected output from saidreceiver for providing a first output in response to a series of pulseshaving said first duration and a second output in response to a seriesof pulses separated by intervals having said first duration, and

indicator means connected to each of said first and second outputs ofsaid pulse sorter means for providing an indication at the remote pointwhenever either of said first or second data pulses occur.

7. A multiplexer as provided in claim 6 wherein said pulse widthmodulator comprises:

an astable multivibrator, and

switching means responsive to said first and second data pulses forselectively changing the u'me constants of said multivibrator.

8. A multiplexer system as recited in claim 7 wherein said astablemultivibrator includes a plurality of timing resistances and saidswitching means comprises a first one-shot responsive to said first datapulse for generating an output pulse having a duration substantiallylonger than either said first or second durations,

a second one-shot responsive to said second data pulse for generating anoutput pulse equal to that generated by said first one-shot,

a first electronic switch connected to said first one-shot and operableto connect a first combination of said timing resistances to saidastable multivibrator,

a second electronic switch connected to said second oneshot and operableto connect a second combination of said timing resistances to saidastable multivibrator,

an AND gate connected to both said first and said second one-shots andproducing an output when the outputs of said first and said secondone-shots are coincident, and

a third electronic switch connected to the output of said AND gate andoperable to connect a third combination of said timing resistances tosaid astable multivibrator.

9. A multiplexer system as recited in claim 8 wherein said receivermeans comprises:

an input tank circuit resonant at the carrier frequency,

a logarithmic amplifier connected to said input tank circuit andproviding an amplified output which emphasizes smaller signalamplitudes,

a tuned amplifier connected to the output of said logarithmic amplifier,and

a threshold detector connected to said tuned amplifier providing anoutput substantially identical to the modulation envelope.

10. A multiplexer system as recited in claim 9 wherein said pulse sortermeans comprises:

first and second pulse width discriminators each operable to detectpulses having said first duration, one of said pulse widthdiscriminators being connected to receive the output of said thresholddetector and the other of said pulse width discriminators beingconnected to receive the inversion of the output of said thresholddetector, and

first and second integrating one-shots connected to respective ones ofthe outputs of said pulse width discriminators for providing outputpulses having durations equal to the duration of the outputs of saidfirst and second one-shots.

11. In a self-service gasoline dispensing system having a plurality ofgasoline pumps each of which are capable of generating trigger pulsescorresponding to fractional parts of units of measurement related to thedispensed gasoline, a remote indicator system comprising a sender foreach pump responsive to the trigger pulses produced thereby andproducing a modulated signal characteristic of its particular pump, eachof said senders being connected to a common powerline,

a receiver for each sender located at a central station and also coupledto said common powerline, each of said receivers being responsive to thecharacteristic modulated signal produced by its corresponding sender,and output means connected to each receiver for producing an indicationof the amount of gasoline dispensed, said output means comprising:

a plurality of one-bit memories, each of said memories being connectedto a respective receiver corresponding to one of said plurality ofgasoline pumps,

strobing means for strobing the outputs of each memory at least twicebetween two consecutive trigger pulses generated by its related pump,and

accumulating means connected to said strobing means for totalizing thetotal number of trigger pulses generated by all of said plurality ofgasoline pumps.

12. A remote indicator system as recited in claim 11,

wherein said strobing means comprises:

a plurality of AND gates each connected to a respective one of saidplurality of one-bit memories,

a clock oscillator, and

a counter connected to said clock oscillator and operative to strobeeach AND gate in succession.

13. A remote indicator system as recited in claim 12 wherein saidaccumulating means comprises:

a flip-flop connected to be toggled back and forth by the combinedoutputs of said AND gates and the output of said clock oscillator,

a stepping motor driven by the outputs of said flip-flop, and

a totalizing counter driven by said stepping motor.

14. A remote indicator system as recited in claim 11 wherein saidstrobing means comprises:

a plurality of AND gates each associated with a respective one of saidplurality of one-bit memories,

said AND gates each having three inputs, the first of said inputsconnected to receive a signal from its associated onebit memory, thesecond of said inputs connected to receive the input signal to saidone-bit memory, and the third of said inputs connected to said strobingmeans whereby an input signal to said one-bit memory prevents said ANDgates from passing a signal.

15. In a self-service gasoline dispensing system having a plurality ofgasoline pumps each of which are capable of generating trigger pulsescorresponding to fractional parts of units of measurement related to thedispensed gasoline, a remote indicator system comprising a sender foreach pump responsive to the trigger pulses produced thereby andproducing a modulated signal characteristic of its particular pump, eachof said senders being connected to a common powerline,

a receiver for each sender located at a central station and also coupledto said common powerline, each of saidsecondary winding of said couplingtransformer and the powerline for blocking the powerline frequency, and

at least one current forcing resistor connected in series between saidcoupling capacitor and said secondary winding.

1 I i i

1. In a dispensing system having at least one dispensing apparatus whichis capable of generating separate triggering pulses corresponding tofractional parts of at least two different units of measurement relatedto the dispensed product, a multiplexer system comprising: a pulse widthmodulator responsive to one of said triggering pulses for generating aseries of pulses having a first duration separated by intervals having asecond duration, said pulse width modulator also being responsive toanother of said triggering pulses for generating a series of pulseshaving said second duration separated by intervals having said firstduration, and said pulse width modulator further being responsive to thesimultaneOus occurrence of the two triggering pulses for generating aseries of pulses having said first duration separated by intervalshaving said first duration, a gated carrier frequency oscillatorconnected to said pulse width modulator and providing a pulse modulatedoutput, transmission means receiving said pulse modulated output fromsaid gated carrier frequency oscillator for transmitting the modulatedsignal to a central point, receiver means at said central point forreceiving the transmitted signal and providing a detected output, pulsesorter means connected to receive the detected output from said receiverfor providing a first output in response to a series of pulses havingsaid first duration and a second output in response to a series ofpulses separated by intervals having said first duration, and indicatormeans connected to each of said first and second outputs of said pulsesorter means for providing an indication at the central point whenevereither of said triggering pulses occur.
 2. A multiplexer system asrecited in claim 1 wherein said pulse width modulator comprises: anastable multivibrator, and switching means responsive to said triggeringpulses for selectively changing the time constants of said astablemultivibrator.
 3. A multiplexer system as recited in claim 2 whereinsaid astable multivibrator includes a plurality of timing resistors andsaid switching means further comprises: a first one-shot triggered byone of said triggering pulses for producing a pulse output having afixed duration substantially longer than both said first and seconddurations, a second one-shot triggered by another of said triggeringpulses for producing an output pulse having a duration equal to that ofthe output of said first one-shot, a first electronic switch connectedto the output of said first one-shot and operable to connect a firstcombination of said timing resistances to said astable multivibrator, asecond electronic switch connected to said second one-shot and operableto connect a second combination of timing resistances to said astablemultivibrator, an AND gate receiving as its inputs the outputs of bothsaid first and said second one-shots and providing an output only whenthe outputs from said first and second one-shots are coincident, and athird electronic switch connected to said AND gate and operable toconnect a third combination of timing resistances to said astablemultivibrator.
 4. A multiplexer system as recited in claim 1 whereinsaid pulse sorter means comprises: first and second pulse widthdiscriminators each operable to detect a pulse having said firstduration, one of said pulse width discriminators receiving the detectedoutput from said receiver means and the other of said pulse widthdiscriminators receiving the inversion of the detected output from saidreceiver means, and first and second integrating one-shots connected tothe output of said first and second pulse width discriminators,respectively.
 5. A multiplexer system as recited in claim 1 wherein saiddispensing apparatus is a gasoline pump and said units of measurementare dollars and gallons, respectively, and said indicator means providesnumerical readouts of the number of gallons dispensed and the dollarvalue thereof.
 6. A multiplexer system comprising a pulse widthmodulator responsive to a first data pulse for generating a series ofpulses having a first duration separated by intervals having a secondduration, said pulse width modulator also being responsive to a seconddata pulse for generating a series of pulses having said second durationseparated by intervals having said first duration, and said pulse widthmodulator further being responsive to the simultaneous occurrence ofsaid first and second data pulses for generating a series of pulseshaving said first duration separated by intervals having said firstduration, a gated carrier frequency oscillator coNnected to said pulsewidth modulator and providing a pulse modulated output, transmissionmeans receiving said pulse modulated output for transmitting themodulated signal to a remote point, receiver means at said remote pointfor receiving the transmitted signal and providing a detected output,pulse sorter means connected to receive the detected output from saidreceiver for providing a first output in response to a series of pulseshaving said first duration and a second output in response to a seriesof pulses separated by intervals having said first duration, andindicator means connected to each of said first and second outputs ofsaid pulse sorter means for providing an indication at the remote pointwhenever either of said first or second data pulses occur.
 7. Amultiplexer as provided in claim 6 wherein said pulse width modulatorcomprises: an astable multivibrator, and switching means responsive tosaid first and second data pulses for selectively changing the timeconstants of said multivibrator.
 8. A multiplexer system as recited inclaim 7 wherein said astable multivibrator includes a plurality oftiming resistances and said switching means comprises a first one-shotresponsive to said first data pulse for generating an output pulsehaving a duration substantially longer than either said first or seconddurations, a second one-shot responsive to said second data pulse forgenerating an output pulse equal to that generated by said firstone-shot, a first electronic switch connected to said first one-shot andoperable to connect a first combination of said timing resistances tosaid astable multivibrator, a second electronic switch connected to saidsecond one-shot and operable to connect a second combination of saidtiming resistances to said astable multivibrator, an AND gate connectedto both said first and said second one-shots and producing an outputwhen the outputs of said first and said second one-shots are coincident,and a third electronic switch connected to the output of said AND gateand operable to connect a third combination of said timing resistancesto said astable multivibrator.
 9. A multiplexer system as recited inclaim 8 wherein said receiver means comprises: an input tank circuitresonant at the carrier frequency, a logarithmic amplifier connected tosaid input tank circuit and providing an amplified output whichemphasizes smaller signal amplitudes, a tuned amplifier connected to theoutput of said logarithmic amplifier, and a threshold detector connectedto said tuned amplifier providing an output substantially identical tothe modulation envelope.
 10. A multiplexer system as recited in claim 9wherein said pulse sorter means comprises: first and second pulse widthdiscriminators each operable to detect pulses having said firstduration, one of said pulse width discriminators being connected toreceive the output of said threshold detector and the other of saidpulse width discriminators being connected to receive the inversion ofthe output of said threshold detector, and first and second integratingone-shots connected to respective ones of the outputs of said pulsewidth discriminators for providing output pulses having durations equalto the duration of the outputs of said first and second one-shots. 11.In a self-service gasoline dispensing system having a plurality ofgasoline pumps each of which are capable of generating trigger pulsescorresponding to fractional parts of units of measurement related to thedispensed gasoline, a remote indicator system comprising a sender foreach pump responsive to the trigger pulses produced thereby andproducing a modulated signal characteristic of its particular pump, eachof said senders being connected to a common powerline, a receiver foreach sender located at a central station and also coupled to said commonpowerline, each of said receivers being responsive tO the characteristicmodulated signal produced by its corresponding sender, and output meansconnected to each receiver for producing an indication of the amount ofgasoline dispensed, said output means comprising: a plurality of one-bitmemories, each of said memories being connected to a respective receivercorresponding to one of said plurality of gasoline pumps, strobing meansfor strobing the outputs of each memory at least twice between twoconsecutive trigger pulses generated by its related pump, andaccumulating means connected to said strobing means for totalizing thetotal number of trigger pulses generated by all of said plurality ofgasoline pumps.
 12. A remote indicator system as recited in claim 11,wherein said strobing means comprises: a plurality of AND gates eachconnected to a respective one of said plurality of one-bit memories, aclock oscillator, and a counter connected to said clock oscillator andoperative to strobe each AND gate in succession.
 13. A remote indicatorsystem as recited in claim 12 wherein said accumulating means comprises:a flip-flop connected to be toggled back and forth by the combinedoutputs of said AND gates and the output of said clock oscillator, astepping motor driven by the outputs of said flip-flop, and a totalizingcounter driven by said stepping motor.
 14. A remote indicator system asrecited in claim 11 wherein said strobing means comprises: a pluralityof AND gates each associated with a respective one of said plurality ofone-bit memories, said AND gates each having three inputs, the first ofsaid inputs connected to receive a signal from its associated one-bitmemory, the second of said inputs connected to receive the input signalto said one-bit memory, and the third of said inputs connected to saidstrobing means whereby an input signal to said one-bit memory preventssaid AND gates from passing a signal.
 15. In a self-service gasolinedispensing system having a plurality of gasoline pumps each of which arecapable of generating trigger pulses corresponding to fractional partsof units of measurement related to the dispensed gasoline, a remoteindicator system comprising a sender for each pump responsive to thetrigger pulses produced thereby and producing a modulated signalcharacteristic of its particular pump, each of said senders beingconnected to a common powerline, a receiver for each sender located at acentral station and also coupled to said common powerline, each of saidreceivers being responsive to the characteristic modulated signalproduced by its corresponding sender, and output means connected to eachreceiver for producing an indication of the amount of gasolinedispensed, each sender being connected to the powerline by a couplingnetwork comprising: a coupling transformer having primary and secondarywindings, said primary winding receiving the output of said sender, acapacitor connected across said primary winding to form a tank circuitresonant at the signal frequency, at least one coupling capacitorconnected in series with the secondary winding of said couplingtransformer and the powerline for blocking the powerline frequency, andat least one current forcing resistor connected in series between saidcoupling capacitor and said secondary winding.